The present invention disclosure relates to methods for the manufacture of bisphenols. In particular, the present invention disclosure relates to methods for improving the efficiency of the manufacture of bisphenols.
Bisphenols are used as raw materials in the preparation of chemical products such as epoxy resins and polycarbonates. They are commonly prepared by the condensation of phenols and ketones in the presence of either an acid catalyst, or an active ion exchange catalyst. Often, a promotor (often referred to as a co-catalyst) is used in the reaction.
Typically the catalysts used in the production of bisphenols undergo rapid deactivation. There are many possible reasons for deactivation, including the presence of excess acetone, bisphenolic tars, and other reaction by-products. Replacing the catalyst is expensive, requires significant labor under adverse conditions, and creates chemical wastes that must be properly disposed of. The use of a promotor while advantageous to the reaction is extremely expensive and any reduction in promotor quantity while maintaining or increasing reactor output is highly desirable.
A particular route for improved bisphenol production and increased catalyst lifetimes involves recycling effluent from the reactor. For example, U.S. Pat. No. 4,308,404 teaches that recycling effluent from any one reactor, which is part of a series, back to the reaction zone, can increase catalyst life. This patent requires however that the reaction zone be constituted of at least two reactors in order to increase catalyst life. Further, it proscribes recycling effluent from the last reactor to the reaction zone.
U.S. Pat. No. 5,786,522 also teaches partial recycling of dehydrated effluent from the reactor back into the input stream in order to produce bisphenols, which are further utilized in polycarbonates to improve color.
Despite a large number of methods proposed for the production of bisphenols, there nonetheless remains a need in the art for effective, efficient methods that are suitable for large-scale, industrial production processes.
A method for the manufacture of bisphenols comprises introducing a combined feed stream comprising a feed stream and a recycle stream into a reactor system comprising at least one reactor containing a catalytic proportion of an acid catalyst and wherein the combined feed stream comprises a carbonyl compound and a stoichiometric excess of phenol; removing from the reactor system a reactor effluent; splitting the reactor effluent into a crystallization feed stream and an effluent recycle stream; extracting from said crystallization feed stream a bisphenol adduct, remainder comprising a mother liquor stream; dehydrating said mother liquor stream and said effluent recycle stream in a dehydrator wherein excess water and carbonyl compound are removed; and recycling the dehydrated mother liquor and the dehydrated effluent recycle stream back to the combined feed stream to effect improved production of p,p-bisphenol, along with increased reactor selectivity and reduced promoter quantities.